Non-intertwined graphitic domains leads to super strong and tough continuous 1D nanostructures

Abstract

A systematic study on mechanics of carbon nanofibers (CNF) in relation to their microstructure is presented. The CNFs were fabricated via pyrolysis of polymeric nanofibers. In order to develop super-strong and super-tough one-dimensional nanomaterials, processing steps were aimed at reducing defects, e.g., poor graphitic alignment. The degree of graphitization was optimally controlled to benefit from strong sp2 C-C bonds while avoiding strength-compromising interactions between graphitic domains. The peculiar feature in CNFs was the discontinuity and rather uniform dispersion of turbostratic domains within the amorphous carbon, an apparent cause of crack pinning, and crack path deflection, thus strengthening/toughening. Hence, our CNFs exhibited superior strength compared to other emerging high-performance continuous fibers, such as CNT and graphene fibers. The best processing condition led to record high average strength of 6.3 ± 0.8 GPa (7.7 GPa maximum), 66% higher than previous reports. Moreover and contrary to most engineering materials, the high strength was achieved at no cost to ductility. The CNF exhibited significant ductility of 3.0 ± 0.7%, with energy-to-failure as high as 86 J/g, the highest reported for graphitic fibers. The research on simultaneously strong and tough CNF provides a promising pathway to develop the next generation of nanoscale reinforcements for lightweight and safety-critical structural applications.